Thermal treatment is a process commonly used in semiconductor manufacturing processes such as logic and storage and in magnetic media manufacturing processes. A substrate is subjected to a programmed heat history to achieve a thermally induced transformation of the material from one state to another. In semiconductor processing, an example is thermally treating a substrate to increase the crystallinity or overall organization of the substrate material. Processes commonly used for thermal treatment include furnace baking, various types of rapid thermal processing, spike annealing and laser processing.
In advanced applications featuring very thin films and/or small critical dimensions, the thermal treatment typically delivers a desired energy dose to the substrate in a very short period of time to avoid undesirable effects from lengthy exposure to thermal energy, such as deep penetration of thermal energy into the substrate and the resulting disruption of underlying layers. Laser processing is commonly selected to access the high power needed for very short processing times.
In laser thermal treatment, a laser beam is directed to a treatment area of a substrate. The radiation field developed by a typical laser has a non-uniform intensity profile. In cross-section, the radiation field has regions of high intensity and regions of low intensity. This non-uniformity results in non-uniform processing of the treatment area, with some parts of the treatment area receiving more energy and some receiving less. These non-uniformities may be quite large, approaching 100% in some cases.
Causes of the non-uniform intensity profile of laser beams are well-known. Lasers are optical oscillators that develop a standing oscillation of energy within the optical cavity of the laser. The standing oscillation is a wave-form having maxima and minima that are realized in the emitted laser beam as modes. These modes may have a spatial component (e.g. maxima and minima distributed across the three-dimensions of space) and/or a temporal component (e.g. maxima and minima that change with time). Additionally, the wave-forms developed in the optical cavity of the laser exhibit interference effects that contribute to the non-uniformity of the emitted energy. Sometimes, these interference effects are called “speckle”. The strongly coherent nature of laser light is uniquely pre-disposed to such interference effects.
Many approaches have been used to address the various manifestations of non-uniformity in laser fields over many decades. In general, the laser beam is subjected to refractive and reflective transformations to blend and/or de-image the modes. Such transformations typically rely on highly designed, expensive optical elements. As device specifications become increasingly demanding, more precise and uniform manufacturing methods are needed. Redesigning optics for each new technology node becomes cost prohibitive. Thus, there is a need in the art for a laser capable of forming an energy field subject to minimal non-uniformity.